The present invention concerns an absorbent fiber web with at least one base layer comprised of cellulose fibers and at least one external layer that is at least over areas thereof connected to the base layer.
In the field of hygiene, fiber webs made from cellulose fibers are widely used. The fiber webs serve as an absorbent core for absorbing bodily fluids. They have the task of absorbing quickly and absorbing permanently the bodily fluids. A further property of a cellulose web is allowing passage of liquids or gases into structures underneath. Since the fiber webs often have direct contact with the body, they should be as compatible as possible with the body and should absorb the incoming liquid in a well distributed fashion. Cellulose has furthermore the advantage that it is biologically decomposable, i.e., it can be disposed of in appropriate landfills where it decomposes without any residue. For their use in hygiene articles, the fiber webs should be highly absorbent or well conducting, should be soft and processable as a web. For increasing the absorption capacity, the fiber matrix has added to it so-called superabsorbers, i.e., polymers that under formation of hydrogels can take up water. The use of the fiber webs in the field of hygiene makes it necessary that the materials for the production of the hygiene articles contain additives and other auxiliary agents only to a limited extent. For processing the fiber webs to absorbent cores, they are usually employed in the form of cellulose nonwovens and airlaid materials. Bonding of the individual cellulose fibers is achieved by binding agents.
Aside from the use in the field of hygiene, the fiber webs can also be used in other areas such as cosmetics or in household applications, for example, for removing dirt or other substances from surfaces as well as for cleansing the skin and for body care. For removing substances from surfaces and also for cleaning purposes, the pure fiber webs are disadvantageous because they have a relatively minimal strength. Moreover, cellulose is a hydrophilic substance that in contact with water absorbs other hydrophilic substances while the absorption and removal of hydrophobic substances is possible only as a result of mechanical rubbing.
The manufacture of binder-free fiber webs is also known. For example, in European patent 1 032 324 B1 a method for producing absorbent and rollable fiber webs comprised of cellulose fibers or cellulose pulp or cellulose cardboard without use of additional binders is disclosed which fiber webs have a tear strength of at least 0.12 kN/m. In the disclosed method a random cellulose fiber layer is provided and precompressed at relatively low pressure so that a loose nonwoven with minimal density and tear strength is produced. This nonwoven is then introduced into the nip of a calander roller pair so that a pattern of dot-shaped or line-shaped pressure areas is produced at relatively high pressure and the randomly positioned fibers are pressed against one another. The fibers are pressed against one another in the calander roller pair at a pressure of 250 to 600 MPa so that a non-detachable fusion of the fibers is realized and on the fiber web an embossment pattern is generated. For producing the fiber webs that are known in the prior art, usually commercially available cellulose fibers are used that, for example, are known by the technical term fluff pulp. In this form of use the cellulose fibers are present in stretched form.
The goal is therefore to produce a fiber web on the basis of cellulose fibers which fiber web is suitable for novel applications because of its specific absorption capability for water.